Here,
we perform structural, thermodynamic, and kinetics tests
of the Kirkwood–Buff-derived force field, KBFF20, for peptides
and proteins developed in the previous article. The physical/structural
tests measure the ability of KBFF20 to capture the experimental J-couplings for small peptides, to keep globular monomeric
and oligomeric proteins folded, and to produce the experimentally
relevant expanded conformational ensembles of intrinsically disordered
proteins. The thermodynamic-based tests probe KBFF20’s ability
to quantify the preferential interactions of sodium chloride around
native β-lactoglobulin and urea around native lysozyme, to reproduce
the melting curves for small helix- and sheet-based peptides, and
to fold the small proteins Trp-cage and Villin. The kinetics-based
tests quantify how well KBFF20 can match the experimental contact
formation rates of small, repeat-sequence peptides of variable lengths
and the rotational diffusion coefficients of globular proteins. The
results suggest that KBFF20 is naturally able to reproduce properties
of both folded and disordered proteins, which we attribute to the
use of the Kirkwood–Buff theory as the foundation of the force
field’s development. However, we show that KBFF20 tends to
lose some well-defined secondary structural elements and increases
the percentage of coil regions, indicating that the perfect balance
of all interactions remains elusive. Nevertheless, we argue that KBFF20
is an improvement over recently modified force fields that require ad hoc interventions to prevent the collapse of intrinsically
disordered proteins.